Integrated circuits (ICs) are common devices in modern electronics. The ICs in a typical personal computer (PC) include a central processing unit (CPU) mounted on a motherboard. The motherboard has connections to couple signals to and from the CPU. CPUs can exchange signals with other ICs such as memory, other processors, application specific ICs (ASICs) and dedicated function IC sets, e.g., chipsets. Some ICs may be mounted on the motherboard with others mounted on another printed circuit board (PCB) coupled therewith.
For performing some computer functions and/or modern applications, the CPU may interact with other processors, which may be mounted on another PCB. Graphics exemplify such a function. Processing related to powerful modern graphics applications can utilize computational resources extensively. It is thus common for modern computers to include a video processor and dedicated memory, etc., typically mounted on a video card ported to the motherboard to readily exchange video, timing, control and other signals with the CPU and related chipsets.
As with other functions exemplified herein with reference to graphics, data and other signals exchanged between processors are transmitted by one IC, the transmitter (Tx) and received by another IC, the receiver (Rx). Certain electrical parameters are significant to such signal exchange. Effective data exchange and other communication between Tx and Rx are thus affected by these electrical parameters.
Significant electrical parameters can include for instance voltage levels, grounding, noise, bias, and connection and interconnection configurations, among others. Due in part to their similar functionality, widespread use and diversified sources of manufacture, many modern computers and other electronics are designed such that they share some electrical parameters in common. Industry standards have been developed to promote such commonality. This can have benefits related to interchangeability.
Continuing with the example of graphics, standards specify electrical parameters that which affect how data is exchanged between the video processor and the chip set associated with the CPU. One such standard is associated with the accelerated graphics port (AGP). The Peripheral Components Interconnect (PCI) standard then developed and even more recently, the PCI Express® (PCIe) standard, promulgated by the PCI Special Interest Group (PCI-SIG) of Portland, Oreg. Another standard, currently under development, is the DisplayPort™ Proposed Standard, promulgated by the Video Electronics Standards Association of Milpitas, Calif.
The PCIe standard is discussed herein as an example. Interconnects compliant with the PCIe standard effectively provide a high performance 32-bit or 64-bit bus (e.g., having physical link widths of 1x, 2x, 4x, 8x and/or 16x) with multiplexed address and data lines.
For alternating current (AC) coupling of signals over interconnects from a transmitting integrated circuit to a remote receiver over an interconnect such as one conforming to the PCIe (and DisplayPort™) specifications, blocking unwanted and/or unmatched direct current (DC) levels and matching impedance between them, and attenuating noise, the PCIe standard specifies that AC coupling capacitors be used on the transmitting end.
Conventional PCIe designs use off-chip discrete capacitors for the AC coupling function. This is required for all transmitting data lines. For bidirectional communication, two transmitting lines are needed for each bus data line, e.g., one for each of the communicating devices. Assuming a 32-bit bus width (e.g., with 16 lanes transmitting and 16 lanes receiving, effectively simultaneously), the conventional design requires 64 off-chip discrete capacitors for AC coupling. The number of discrete components unfortunately consumes space on the PCB that could be used for other functionality and/or reduce the size of the PCB.